Field
The disclosed concept relates to electrical switching apparatus, such as, for example, circuit breakers and, more particularly, to circuit breakers employing arc chamber assemblies. The disclosed concept also relates to arc chamber assemblies for circuit breakers. The disclosed concept further relates to circuit protection methods.
Background Information
Electrical switching apparatus, such as circuit breakers, are employed in diverse capacities in power distribution systems. A circuit breaker may include, for example, a line conductor, a load conductor, a fixed contact and a movable contact, with the movable contact being movable into and out of electrically conductive engagement with the fixed contact. This switches the circuit breaker between an ON or closed position and an OFF or open position, or between the ON or closed position and a tripped or tripped OFF position. The fixed contact is electrically conductively engaged with one of the line and load conductors, and the movable contact is electrically conductively engaged with the other of the line and load conductors. The circuit breaker may also include an operating mechanism having a movable contact arm upon which the movable contact is disposed. Upon initial separation of the movable contact away from the stationary contact, an electrical arc is formed in the space between the contacts. The arc provides a means for smoothly transitioning from a closed circuit to an open circuit, but produces a number of challenges to the circuit breaker designer. Among them is the fact that the arc results in the undesirable flow of electrical current through the circuit breaker to the load. Additionally, the arc, which extends between the contacts, often results in vaporization or sublimation of the contact material itself. Therefore, it is desirable to extinguish any such arcs as soon as possible upon their propagation.
To facilitate this process, circuit breakers typically include arc chutes which are structured to attract, cool, and split the arcs. Specifically, each arc chute includes a plurality of spaced apart metallic or non-metallic splitter plates. As the movable contact is moved away from the stationary contact, the movable contact moves past the ends of the splitter plates, with the arc being drawn by magnetic and fluid-dynamic forces toward and between the splitter plates. The splitter plates are electrically insulated from one another such that the arc is quenched and split into several short arcs in series burning between the splitter plates, which generates a relatively high arc voltage until the arc is extinguished. In order to successfully interrupt a DC circuit, the circuit breaker needs to generate an arc voltage higher than the system voltage to stop the current flow. A challenge with interruption is that there is often not enough magnetic force to successfully draw the electrical arc into the arc chute. For example, many known arc chamber assemblies are able to draw the electrical arc towards the splitter plates at only relatively low current levels or relatively high current levels, but not at both low current levels and at high current levels.
There is thus room for improvement in electrical switching apparatus, and in arc chamber assemblies and in associated circuit protection methods.